This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Mother-to-child transmission of HIV is a significant cause of infant mortality and morbidity worldwide, reversing the decades of progress in infant survival. We have been studying the role of maternal neutralizing antibodies (NAbs) in limiting infection or pathogenesis. We infected newborn infant macaques orally with pathogenic SHIV and administered passively acquired SHIV-specific IgG to simulate maternal IgG. We monitored the disease course and the immune responses generated to SHIV in the newborns. We compared neutralizing IgG Matched to the challenge virus and Mismatched IgG with limited neutralizing activity against the challenge virus.